Various liquids, including hazardous liquid materials, are often stored and transported in drums, particularly drums of the 55 gallon type. Drums utilized for transporting of hazardous liquid materials are subject to rules and regulations of governmental regulatory bodies, such as the Department of Transportation in the United States. These rules and regulations require drum constructions to withstand breakage during drop and tip tests.
A 55 gallon drum can weigh as much as 880 pounds under acceptable regulations and it is therefore necessary for the manufacturer to provide the user with some means of moving the drum. The steel drum industry has developed a device called a "parrot beak" lifting device, which acts like a parrot's beak and squeezes the top chime or handling ring of a drum enough that it will not slip when the drum is lifted using the device. The device acts by both compressing the handling ring between its jaws as well as digging into its surface. Steel drums are more and more frequently being replaced by plastic drums throughout the industry for various reasons well known to those in this industry. The same parrot beak lifting device is the tool of choice for handling and lifting of filled plastic drums.
Heretofore, there have been several manufacturing methods utilized in providing plastic drums with a parrot beakable handling ring. One such manufacturing method is to shrink-fit a plastic ring onto a blow-molded plastic drum so tightly that, given the weight placed in the drum, it will not slip off because the compressive forces on the drum/ring interface are so large that they overcome the stresses of lifting the assembly via the ring. Other manufacturing methods have included injection molding an entire drum head with an integral handling ring and then sonic welding or hot plate welding such injection molded drum head onto a blow-molded or otherwise formed drum, thus yielding a closed drum with an integral handling ring for transporting liquid hazardous material. Problems have been presented with both these types of drums and manufacturing processes from an economic standpoint and from the standpoint of providing a construction which will satisfactorily withstand breakage due to forces created during dropping or tipping of a filled drum.
A further preferred manufacturing method for such a plastic drum with a handling ring would include blow-molding of a drum having a closed head with an integral handling ring extending therefrom and formed by being compression-molded through the use of an articulating section in the blow mold. Such blow-molded drums with compression-molded handling rings have also suffered from problems relating to breakage of the drum upon impact during dropping or tipping of a filled drum. The blow-molding processing considerations heretofore utilized have not taken into account stresses caused by such dropping or tipping. Specifically, current designs of drums and their manufacturing processes do not consider the effects of the flow of plastic material inside the drum during compression-molding ring formation processes, which creates stress concentrations which limit the usefulness of the drum and resistance to breaking during dropping or tipping. Stress concentration points are created due to the flow of residual materials from the compression-molding of the integral handling ring unless the direction of flow and the location of the resultant extrudate is carefully controlled. Also, current drum designs place the outside surface of the handling ring outwardly of the outside surface of the drum body which causes an inordinate amount of force on the handling ring when a filled drum is dropped or tipped which causes breakage of the drum particularly at the stress concentration points.